Wee welcome all those who are interested to join us on Tuesdays, 3:00–4:00 PM, Ryerson Laboratory, Room 358, unless noted otherwise.

Everyone is also invited to attend the Learning Seminar on Geometric Analysis, organized by Prof. Andre Neves. More information on http://www.math.uchicago.edu/~geometric_analysis/learning

Shmuel Weinberger, The University of Chicago

**
Persistent Homology and Gromov's theorem on closed contractible geodesics.
:**
Gromov showed that on any closed Riemannian manifold whose fundamental group has unsolvable word problem, there are infinitely many closed nullhomotopic geodesics (of index 0). I will explain this theorem from the point of Persistent Homology of the free loop space, and then give some refinements (e.g. to less exotic fundamental groups) and extensions (to some other functionals other than energy on loops).

David Wiygul, UC Irvine

**
The Bartnik-Bray outer mass of small spheres
:**
In 1989 Robert Bartnik proposed a definition of quasilocal mass
in general relativity. The Bartnik mass is known to enjoy several
attractive properties but is not straightforward to evaluate. I will talk
about a first-order estimate for a natural modification of Bartnik's
definition applied to small perturbations of spheres in Euclidean space.
In particular I will describe an application to the small-sphere limit in
time-symmetric slices.

Nick Edelen , MIT

**
Quantitative Reifenberg for Measures
:**
In joint work with Aaron Naber and Daniele Valtorta, we
demonstrate a quantitative structure theorem for measures in R^n under
assumptions on the Jones \beta-numbers, which measure how close the
support is to being contained in a subspace. Measures with this property
have arisen in several interesting scenarios: in obtaining packing
estimates on and rectifiability of the singular set of minimal surfaces;
in characterizing L2-boundedness of Calderon-Zygmund operators; and as
an "annalist's" formulation of the travelling salesman problem.

Dan Ketover , Princeton University

**
Free boundary minimal surfaces of unbounded genus
:**
Free boundary minimal surfaces are natural variational objects
that have been studied since the 40s. In spite of this, very few explicit examples in
the simplest case of the round three ball are known. I will describe how variational
methods can be used to construct new examples with unbounded genus resembling a
desingularization of the critical catenoid and flat disk. I will also give a new variational
interpretation of the previously known examples.

Marco Radeschi , University of Notre Dame

**
Minimal hypersurfaces in compact symmetric spaces
:**
A conjecture of Marques-Neves-Schoen says that for every
embedded minimal hypersurface M in a manifold of positive Ricci curvature,
the first Betti number of M is bounded above linearly by the index of M.
We will show that for every compact symmetric space this result holds, up
to replacing the index of M with its extended index. Moreover, for special
symmetric spaces, the actual conjecture holds for all metrics in a
neighbourhood of the canonical one. These results are a joint work with R.
Mendes.

Pierre Albin , University of Illinois at Urbana-Champaign

**
Analytic torsion of manifolds with fibered cusps
:**
Analytic torsion is a spectral invariant of the Hodge Laplacian
of a manifold with a flat connection. On a closed manifold it is equal to
a topological invariant known as Reidemeister torsion. I will describe joint
work with Frédéric Rochon and David Sher establishing a topological
expression for the analytic torsion of a manifold with fibered cusp ends
(such as a locally symmetric space of rank one). We establish our result by
controlling the behavior of the spectrum along a degenerating class of
Riemannian metrics.

Jacob Bernstein , Johns Hopkins University

**
Surfaces of Low Entropy
:**
Following Colding and Minicozzi, we consider the entropy of
(hyper)-surfaces in Euclidean space. This is a numerical measure of the
geometric complexity of the surface and is intimately tied to to the
singularity formation of the mean curvature flow. In this talk, I will
discuss several results that show that closed surfaces for which the
entropy is small are simple in various senses. This is all joint work with
L. Wang.

Pedro Gaspar , IMPA

**
Minimal hypersurfaces and the Allen-Cahn equation on closed manifolds
:**
Since the late 70s parallels between the theory of phase transitions and critical points of the area functional have helped us to understand variational properties of certain semi-linear elliptic PDEs and spaces of hypersurfaces which minimize the area in an appropriate sense. We will discuss some recent developments in this direction which extend well-known analogies regarding minimizers to more general variational solutions. In particular, borrowing ideas from the min-max theory of minimal hypersurfaces, we study the number of solutions of the Allen-Cahn equation in a closed manifolds and solutions with least non-trivial energy.

Or Hershkovits , Stanford University

**
Uniqueness of mean curvature flow with mean convex singularities
:**
Given a smooth compact hypersurface in Euclidean space, one can
show that there exists a unique smooth evolution starting from it,
existing for some maximal time. But what happens after the flow becomes
singular? There are several notions through which one can describe weak
evolutions past singularities, with various relationship between them.
One such notion is that of the level set flow. While the level set flow is
almost by definition unique, it has an undesirable phenomenon called
fattening: Our "weak evolution" of n-dimensional hypersurfaces may develop
(and does develop in some cases) an interior in R^{n+1}. This fattening
is, in many ways, the right notion of non-uniqueness for weak mean
curvature.
As was alluded to above, fattening can not occur as long as the flow is
smooth. Thus it is reasonable to say that the source of fattening is
singularities. Permitting singularities, it is very easy to show that
fattening does not occur if the initial hypersurface, and thus all the
evolved hypersurface, are mean convex. Thus, singularities encountered
during mean convex mean curvature flow should be of the kind that does not
create singularities (i.e, the local structure of the singularities should
prevent fattening, without any global mean convexity assumption). To put
differently, it is reasonable to conjecture that:
"An evolving surface cannot fatten unless it has a singularity with no
spacetime neighborhood in which the surface is mean convex".
In this talk, we will phrase a concrete formulation of this conjecture,
and describe its proof. This is a joint work with Brian White.

Xin Zhou , MIT

**
Min-max minimal hypersurfaces with free boundary
:**
I will present a joint work with Martin Li. Minimal surfaces
with free boundary are natural critical points of the area functional in
compact smooth manifolds with boundary. In this talk, I will describe a
general existence theory for minimal surfaces with free boundary. In
particular, I will show the existence of a smooth embedded minimal
hypersurface with free boundary in any compact smooth Euclidean domain. The
minimal surfaces with free boundary were constructed using the min-max
method.
Our result allows the min-max free boundary minimal hypersurface to be
improper; nonetheless the hypersurface is still regular.

Henrik Matthiesen , Max Plank Institute for Mathematics Bonn

**
Existence of metrics maximizing the first eigenvalue on closed
surfaces
:**
We show that on each closed surface of fixed topological type,
orientable or non-orientable, there is a metric, smooth away from finitely many conical singularities,
that maximizes the first eigenvalue among all unit area metrics. The key new ingredient are
several monotonicity results relating the corresponding maximal eigenvalues. This is joint work with Anna Siffert.

Gang Liu, Northwestern University

**
On some recent progress of Yau's uniformization conjecture
:**
Yau's uniformization conjecture states that a complete noncompact Kahler manifold with positive bisectional
curvature is biholomorphic to the complex Euclidean space. We shall discuss some recent progress via the Gromov-Hausdorff
convergence technique.

John Ma, University of British Columbia

**
**** Compactness, finiteness properties of Lagrangian self-shrinkers in R^4 and Piecewise mean curvature flow.
:**
In this talk, we discuss a compactness result on the space of compact Lagrangian self-shrinkers in R^4. When the area is bounded above
uniformly, we prove that the entropy for the Lagrangian self-shrinking tori can only take finitely many values; this is done by deriving a
Lojasiewicz-Simon type gradient inequality for the branched conformal self-shrinking tori. Using the finiteness of entropy values, we construct a
piecewise Lagrangian mean curvature flow for Lagrangian immersed tori in R^4, along which the Lagrangian condition is preserved, area is
decreasing, and the type I singularities that are compact with a fixed area upper bound can be perturbed away in finite steps. This is a Lagrangian
version of the construction for embedded surfaces in R^3 by Colding and Minicozzi. This is a joint work with Jingyi Chen.

Laura Schaposnik, University of Illinois at Chicago

**
On the geometry of branes in the moduli space of Higgs bundles.
:**
After giving a gentle introduction to Higgs bundles, their moduli space and the associated Hitchin fibration,
I shall describe how actions both on groups and on surfaces (anti-holomorphic or of finite groups) lead to families of interesting
subspaces of the moduli space of Higgs bundles (the so-called branes). Finally, we shall look at correspondences between these branes
that arise from Langlands duality, as well as from other relations between Lie groups.

Pei-Ken Hung, Columbia University

**
**** A Minkowski inequality for hypersurfaces in the Anti-deSitter-Schwarzschild manifold
:**
We prove a sharp inequality for hypersurfaces in the
Anti-deSitter-Schwarzschild manifold. This inequality generalizes the
classical Minkowski inequality for surfaces in the three dimensional
Euclidean space, and has a natural interpretation in terms of the Penrose
inequality for collapsing null shells of dust. The proof relies on a
monotonicity formula for inverse mean curvature flow, and uses a geometric
inequality established by Brendle.

Lan-Hsuan Huang, University of Connecticut

**
Geometry of Static Asymptotically Flat 3-Manifolds
:**
A static potential on a 3-manifold reflects the symmetry of the spacetime development and is
also closely related to the scalar curvature deformation.
We discuss how minimal surfaces of 3-manifold interact with the static potential and, as an application,
give a new proof to the rigidity of the Riemannian positive mass theorem.

Yu Li, University of Wisconsin-Madison

**
Ricci flow on asymptotically Euclidean manifolds
:**
In this talk, we prove that if an asymptotically Euclidean (AE) manifold with nonnegative scalar curvature has long
time existence of Ricci flow, it converges to the Euclidean space in the strong sense. By convergence, the mass will drop to
zero as time tends to infinity. Moreover, in three dimensional case, we use Ricci flow with surgery to give an independent
proof of positive mass theorem.

Yannick Sire, Johns Hopkins University

**
Bounds on eigenvalues on Riemannian surfaces
:**
In a joint program with N. Nadirashvili, we developed some tools to prove
existence of extremal metrics in conformal classes for eigenvalues of the Laplace-Beltrami operator on surfaces.
I will describe these results and move to an application to the isoperimetric inequality of the third eigenvalue on the 2-sphere.

Henri Roesch, Duke University

**
Proof of a Null Penrose conjecture using a new Quasi-local Mass
:**
We define an explicit quasi-local mass functional which is non-decreasing along all
foliations (satisfying a convexity assumption) of null cones. We use this new functional to prove the null Penrose conjecture
under fairly generic conditions.

Luca Spolaor, MIT

**
A direct approach to an epiperimetric inequality for Free-Boundary problems
:**
Using a direct approach, we prove a 2-dimensional epiperimetric inequality for the one-phase problem in the scalar and vectorial cases and
for the double-phase problem. From this we deduce the $C^{1,\alpha}$ regularity of the free-boundary in the scalar one-phase and double-phase
problems, and of the reduced free-boundary in the vectorial case, without any restriction on the sign of the component functions. In this talk I
will try to explain the proof of the epiperimetric inequality in the scalar one-phase problem. This is joint work with Bozhidar Velichkov.

Victoria Sadovskaya, Department of Mathematics - Penn State

**Boundedness, compactness, and invariant norms for operator-valued cocycles.:**
We consider group-valued cocycles over dynamical systems with
hyperbolic behavior, such as hyperbolic diffeomorphisms or subshifts
of finite type. The cocycle A takes values in the group of invertible
bounded linear operators on a Banach space and is Holder continuous.
We consider the periodic data of A, i.e. the set of its return values
along the periodic orbits in the base. We show that if the periodic data
of A is bounded or contained in a compact set, then so is the cocycle.
Moreover, in the latter case the cocycle is isometric with respect to
a Holder continuous family of norms. This is joint work with B. Kalinin.

Baris Coskunuser , Boston College

**
Embeddedness of the solutions to the H-Plateau Problem
:**
In this talk, we will give a generalization of Meeks and Yau's embeddedness result on the solutions of the Plateau
problem to the constant mean curvature disks. arXiv:1504.00661

Lu Wang, Department of Mathematics - University of Wisconsin-Madison

**Asymptotic structure of self-shrinkers:**
We show that each end of a noncompact self-shrinker in Euclidean
3-space of finite topology is smoothly asymptotic to a regular cone or a
self-shrinking round cylinder.

Spencer Becker-Kahn, Department of Mathematics - MIT

**Zero Sets of Smooth Functions and p-Sweepouts:**
It is well known that any closed set can occur as the zero set of a smooth function. But in many contexts in analysis, one does not work with arbitrary smooth functions; one works with smooth functions that vanish to only finite order. And the zero set of any such function must have some regularity and structure.
With recourse to an analogy made by Gromov and some recent conjectures of Marques and Neves, I will explain the application of some general results about such zero sets to p-sweepouts (which are p-dimensional families of generalized hypersurfaces that sweepout a smooth manifold in a certain sense). In the course of doing so, I will explain a new result about the regularity of zero sets of smooth functions near a point of finite vanishing order (joint work with Tom Beck and Boris Hanin)..

Jonathan Zhu, Department of Mathematics - Harvard University

**
Entropy and self-shrinkers of the mean curvature flow:**
The Colding-Minicozzi entropy is an important tool for understanding the mean curvature flow (MCF), and is a measure of the complexity of a submanifold. Together with Ilmanen and White, they conjectured that the round sphere minimises entropy amongst all closed hypersurfaces. We will review the basics of MCF and their theory of generic MCF, then describe the resolution of the above conjecture, due to J. Bernstein and L. Wang for dimensions up to six and recently claimed by the speaker for all remaining dimensions. A key ingredient in the latter is the classification of entropy-stable self-shrinkers that may have a small singular set.

Greg Chambers, Department of Mathematics - The University of Chicago

**
Existence of minimal hypersurfaces in non-compact manifolds:**
I prove that every complete non-compact manifold of finite volume admits a minimal hypersurface of finite area. This work
is in collaboration with Yevgeny Liokumovich.

Peter McGrath, Brown University

**
New doubling constructions for minimal surfaces:**
I will discuss recent work (with Nikolaos Kapouleas) on constructions of new embedded minimal surfaces using singular perturbation
'gluing' methods. I will discuss at length doublings of the equatorial S^2 in S^3. In contrast to earlier work of Kapouleas, the catenoidal bridges
may be placed on arbitrarily many parallel circles on the base S^2. This necessitates a more detailed understanding of the linearized problem and
more exacting estimates on associated linearized doubling solutions.

Franco Vargas Pallete, UC Berkeley

**
Renormalized volume:**
The renormalized volume V_R is a finite quantity associated to certain hyperbolic 3-manifolds of infinite volume. In this talk I'll discuss its definition and some properties for acylindrical manifolds, namely local convexity and convergence under geometric limits. If time suffices I'll also discuss some applications and further examples.

Christos Mantoulidis, Stanford University

**
Fill-ins, extensions, scalar curvature, and quasilocal mass:**
There is a special relationship between the Jacobi and the ambient scalar curvature operator. I'll talk about an extremal bending technique that exploits this relationship. It lets us compute the Bartnik mass of apparent horizons and disprove a form of the Hoop conjecture due to G. Gibbons. Then, I'll talk about a derived "cut-and-fill" technique that simplifies 3-manifolds of nonnegative scalar curvature. It is used in studying a priori L^1 estimates for boundary mean curvature for compact initial data sets, and in generalizing Brown-York mass. Parts of this talk reflect work done jointly with R. Schoen/P. Miao.

Hung Tran, UC Irvine

**
Index Characterization for Free Boundary Minimal Surfaces:**
A FBMS in the unit Euclidean ball is a critical point of the area functional among all surfaces with boundaries in the unit sphere, the boundary of the ball. The Morse index gives the number of distinct admissible deformations which decrease the area to second order. In this talk, we explain how to compute the index from data of two simpler problems. The first one is the corresponding problem with fixed boundary condition; and the second is associated with the Dirichlet-to-Neumann map for Jacobi fields. We also discuss applications to a conjecture about FBMS with index 4.

For further information on this seminar or this webpage, please contact Marco Guaraco at
`guaraco(at)math.uchicago.edu`, Lucas Ambrozio at
`lambrozio(at)math.uchicago.edu` or
Rafael Montezuma at `montezuma(at)math.uchicago.edu`